1. Field of the Invention
The present invention relates to cooling system for centrifuges, and more particularly to an improved refrigerant cooling coil assembly for a centrifuge chamber.
2. Description of Related Art
Centrifugation generally involves rotating a sample solution at high speed about an axis to create a high centrifugal field to separate the sample into its components based upon their relative specific gravity. Referring to FIG. 1, the sample is carried in a rotor 10 which is placed in a centrifuge chamber 12 in a centrifuge instrument. The rotor 10 is driven to rotate at high speed by a motor 14 beneath the centrifuge chamber 12. At high speed operations, e.g. greater than 10,000 rpm, aerodynamic drag on the rotor becomes significant. Significantly more power is required to overcome the aerodynamic drag at high speed. In addition, cooling means should be provided to offset the heat generated by aerodynamic friction. Some centrifuges are provided with means for drawing a vacuum or partial vacuum in the Centrifuge chamber in an effort to reduce the aerodynamic drag; however, cooling is still essential.
In the past, cooling of the centrifuge chamber has been accomplished by attaching refrigerant coils to the outside of the centrifuge chamber. Referring to FIGS. 1 and 2, two prior art methods of attaching the refrigerant coils are shown. In FIG. 1, the refrigerant "coils" are in the form of passages 16 formed by welding a corrugated sleeve 18 around the centrifuge chamber 12. (The size of the corrugations are exaggerated in the illustration.) A refrigeration unit 17 circulates refrigerant through the passages 16 between the sleeve 18 and the outside wall of the centrifuge chamber 12. In this prior art configuration, a space must be provided between adjacent passages to allow for welding (e.g. at 19 and 20) which reduces available surface area for efficient heat transferred from the chamber.
In FIG. 2, circular refrigerant tubing 22 is soldered to the outside wall of the centrifuge chamber 12. Adjacent sections of the tubing 22 are spaced apart to provide clearance for applying solder 23. (The size and spacing of the tubing is exaggerated in the illustration.) This spacing reduces the surface area that is available for heat transfer. In addition, differences in thermal expansion and contraction between the centrifuge chamber, the refrigerant tubing and the solder material may cause fracture in the solder joint thereby reducing the contact between the refrigerant tubing and the wall of the centrifuge chamber 12.